1. Field of the Invention
The present invention relates to a pile forming method and apparatus for a pile fabric weaving machine in which piles are formed by changing the relative distance between the reed beating position and the cloth fell of woven fabric.
2. Description of the Prior Art
As a method of forming piles by changing the relative distance between the reed beating position and the cloth fell of woven fabric, there are mentioned a method of changing the reed beating position and a method of changing the cloth fell by shifting or displacing the path along which the fabric is moved (hereinafter referred to as the cloth path). In Japanese Unexamined Patent Application Publications Nos. 73141/1981, 47337/1990 and 156546/1993 (JP-A-56-73141, JP-A-H2-47337 and JP-A-H5-156546), there is disclosed a pile fabric weaving machine in which the cloth fell position is changed by displacing the cloth path.
In the case of the pile fabric weaving machine disclosed in JP-A-H2-47337, a worm wheel portion is formed in a supporting lever on which an expansion bar is supported, wherein a worm mounted fixedly on an output shaft of a servo motor meshes with the worm wheel portion. Through forward/backward rotations of the servo motor, the expansion bar is swingably displaced, whereby the cloth fell position is changed.
However, there exists inevitably a backlash between the worm and the worm wheel, as a result of which a large sliding load acts between the worm and the worm wheel upon changing-over of the rotating direction of the servo motor between the forward direction and the backward or reverse direction. Owing to this sliding load, there is friction between the worm and the worm wheel, which friction tends to further increase the backlash between the worm and the worm wheel. As a result of this, the position of the expansion bar deviates from the normal positions predetermined for a fast pick operation and a loose pick operation, respectively. More specifically, in the fast pick operation phase, the cloth fell position is displaced in the direction in which the beating force of the reed increases, while in the loose pick operation phase, the cloth fell position is displaced in the direction in which the distance between the cloth fell position and the reed beating position increases. When these displacements occur, the beating force of the reed becomes excessively large and the amount of terry consumed for the formation of the piles changes or increases. It goes without saying that an excessively large beating force of the reed and variation in the amount of terry exert adverse influence upon the formation of piles, incurring degradation in the quality of the pile fabric as manufactured.
Further, because of the large sliding load mentioned above, efficiency in the transmission of driving power between the worm and the worm wheel is degraded, involving a large load applied to the servo motor. Under the circumstances, an electric motor of a large capacity has to be employed as the servo motor, which is of course undesirable not only from the economical viewpoint but also in the respect that a large space is required for installation. On the other hand, in the case of the pile fabric weaving machine disclosed in JP-A-56-73141 mentioned above, a surface roller constituting one of the members which form or define the cloth path is arranged to be switchably driven by a terry motion mechanism, whereas in the case of the pile fabric weaving machine disclosed in JP-A-H5-156546, an expansion bar constituting one of the cloth path defining members is switchably driven by a terry motion mechanism.
It is self-explanatory that the conditions for the pile formation exert great influence upon the quality of the pile fabric manufactured by the pile fabric weaving machine. In the case where the piles are to be formed only to one surface of the fabric, there may occur such a pile dropout event that a pile is formed on the other surface of the fabric. Certainly, in the pile fabric weaving machines disclosed in JP-A-56-73141 and JP-A-H5-156546, the pile length can be changed in the course of the weaving operation. However. in these prior art machines, it is noted that no measures are taken concerning the pile formation on which the quality of the pile fabric has great dependency.